Micrometre

A micrometre is one-millionth of a metre (1/1000 of a millimetre, or 0.001 mm). Its unit symbol in the International System of Units (SI) is μm.

The term micron and the symbol μ, representing the micrometre were officially accepted between 1879 and 1967, but officially revoked by the ISI in 1967.

In practice, micron is a widely used term in preference to micrometre in many English-speaking countries, and in American English the use of the term helps differentiate the unit from the micrometer, a measuring device, which would otherwise be spelled as a homonym with micrometre. The term micron has particular currency in science, and is extensively used in most English-speaking countries in the fields of geology, biology, physics, astronomy, and the semiconductor industry.

The micrometre is a common unit of measurement for wavelengths of infrared radiation.